1. Field of the Invention
This invention relates to the field of burglar alarms, and particularly to wireless reed switch-based burglar alarms.
2. Description of the Related Art
Reed switch-based burglar alarms are well-known and widely used. Conventionally, such alarms are mounted adjacent to a movable structure such as a door or window. The movable structure provides access to a space to be protected, such as a home, a business, or a warehouse. The burglar alarm is housed within an enclosure which includes a magnetic reed switchxe2x80x94i.e., a long, thin switch which is actuated by means of a magnet brought near and oriented along the length of the switch. An actuating magnet is mounted to the movable structure and oriented such that, when closed (thereby blocking access to the protected space), the reed switch is actuated, and when opened, the reed switch is de-actuated. Circuitry monitors the switch""s actuation state to detect an unauthorized entry attempt.
An unauthorized entry attempt may be signaled in any of several ways. For example, an audible and/or visible indicator may be built into the alarm unit. Alternatively, the monitoring circuitry may generate a signal which is conveyed to a remote receiver which receives the signal and provides an alarm indication.
A burglar alarm of this sort is typically mounted on the inside of the protected space; this is done to prevent tampering, and to protect the alarm from the elements. However, this approach can have a number of drawbacks in applications in which access to the inside of the protected space is not readily available. For example, a renter of a mini-storage unit may wish to protect his goods with a burglar alarm, but does not wish to grant regular access to the inside of his space. In such a situation, necessary or routine maintenance or repair of the alarm unit may be impossible, which can result in unauthorized entry into the space with no alarm indication.
A reed switch-based burglar alarm is presented which overcomes the problems noted above. The alarm provides several mounting options, including that of mounting on the outside of the space being protected.
The novel burglar alarm features two reed switches mounted perpendicularly to each other within the alarm enclosure. The orientations of the perpendicular reed switches permit the enclosure to be mounted in alternate ways with respect to the movable structure being monitored. The alarm is preferably housed within a parallelepiped enclosure, with one of the enclosure""s sides adapted for mounting to a surface. The first reed switch lies in a plane parallel to the surface to which the alarm is mounted, and the second reed switch lies in a plane perpendicular to the mounting surface. Thus, a magnet can be mounted on a swing-out type door and the alarm enclosure mounted on a wall adjacent to the door such that the magnet actuates the first reed switch when the door is closed. Similarly, a magnet can be mounted on a roll-up type door and the enclosure mounted to a surface perpendicular to the door (such as the door jamb) such that the magnet actuates the second reed switch when the door is closed. This arrangement provides the present alarm an unprecedented level of mounting flexibility.
Several features are described which facilitate using the present alarm on the outside of the protected space. The alarm""s enclosure is preferably made impact and weather-resistant. The present alarm is preferably made wireless, to eliminate the presence of hard-wiring which can become damaged. An anti-tamper reed switch can be used to detect the presence of a rogue magnet intended to keep the alarm from sounding when the movable structure is being moved. Another anti-tamper reed switch can be used to indicate that the cover of the enclosure has been removed.
Further features and advantages of the invention will be apparent to those skilled in the art from the following detailed description, taken together with the accompanying drawings.